Ito Kosuke

Thank you for your reply.

If you leave it as it is, it will be distributed to unsupported WordPress environments. You should drop the current version and set the Requires at least header to the plugin.

I got the same error in my environment.

It’s probably a mistake in add_action instead of do_action.

I’ve created modified version of this plugin. It supports WordPress 5.9’s FSE. How to send this?